The present invention relates to a method for testing the radiation hardness of electronic components. This testing has high economic and industrial relevance because electronic components on board of satellites, space vessels, aircraft (“missiles”) and in Earth-based nuclear facilities can be subject to extreme irradiation by different forms of radiation which can lead to malfunction of electronic devices and circuits if they are not adequately designed.
Each spaceship, each probe, each aircraft and, above all, each satellite is packed with electronic components. These components are critically important for the functioning of the missile. For this reason, the resistance of electronic components to be used on board missiles against various types of space radiation is tested extensively prior to launch. Moreover, it is not enough to test a certain electronic component only once. Due to variations found in the quality of different production batches of electronic components, it is typically desirable to conduct tests of electronic components intended for use each time a missile is assembled.
Electronic components such as computer chips, random access memory (RAM), transistors, solar cells and the like are sensitive to particle beams, such as beams of electrons, ions, protons, neutrons and other elementary particles, and are also sensitive to photon radiation such as x-rays. Such types of radiation can occur in space, and at high altitudes, with high intensity. (As used herein, the term “space” is used to refer to any aspect of space when radiation is a matter of concern.) The multiplicity of types of radiation in space is due to the fact that there are many different sources of radiation in space, and different mechanisms can underly the generation and acceleration of particles and other radiation in space.
For example, it is well-known that in the van Allen radiation belts (such as are illustrated in FIG. 2C, intense beams of so called “killer electrons” can occur. These sudden bursts of intense, high-energy electrons can be extremely destructive to both man and machine. Within the inner van Allen belt, it is mostly protons and ions that are collected and accelerated. These can be highly dangerous to spacecraft. However, encounters with high-energetic electrons occur mainly in the outer van Allen belt, where Medium Earth Orbit (MEO) satellites such as GPS satellites are positioned. The distance and the extent of the van Allen belts can vary substantially, so that lower and higher orbits can be affected, including geosynchronous orbits. Further, other astrophysical objects with magnetic fields such as Jupiter, Saturn etc. also create radiation belt electrons that might pose a danger to spacecraft.
The mechanisms for the acceleration of these relativistic electrons have been subject to intense discussion in recent years. According to NASA standard models AE8/AP8, accelerated and trapped electrons and protons in space have exponential, or “power-law,” energy distributions. This fact means that most particles have relatively low energies, and fewer electrons have higher energies capable of deep penetration. The detailed process of how, for example, the electrons penetrate missile shielding and accumulate in insulations around satellite electronics, eventually causing catastrophic internal dielectric discharges, is strongly dependent on the energy distribution of the incoming energy flux. FIG. 2A shows two examples of electron energy spectra that can be expected to be encountered in space, calculated based on the AE8 model. One is calculated for an McIlwain parameter of L=2 during solar activity minima (AE8 min), the other for L=3 during solar activity maxima (AE8max). What is notable about FIG. 2A is that the distribution of the energy spectra shown is that they follow an exponential, or a power law, distribution. This fact is of significance to the present invention and its relevance will become apparent herein.
Similar exponential distributions occur in space elsewhere than in the Earth's van Allen belts and, in the radiation belts of other planets such as Jupiter, the electron energies can reach significantly higher levels than those in the van Allen belts. Energetic electrons can damage electronics in multiple ways, such as via the total ionizing dose (TID), or single event effects (SEE). Single event effects (SEE) are gaining increasing significance, as semiconductor structures are getting smaller. These single events triggered by bombardment of particles can have large detrimental effects and can be highly complex. Important SEE effects include:                Single Event Upsets (SEU). SEU are basically bit-flips, which occur when an energetic particle causes, for example, the state of a transistor in an electronic circuit to reverse. These phenomena can occur in nearly all microcircuits, microprocessors and memory chips.        Single Event Latchups (SEL). Energetic charged particles can activate parasitic transistors, which can then combine into a circuit with a large positive feedback, resulting in a short.        
FIG. 2D illustrates how an unwanted pulse is generated by an SEU. An energetic particle leaves behind an ionization track in a transistor. The relevant charges produced along this track are mainly in the form of electrons and electron holes. These charges are collected at the source and at the drain, which results in a current pulse emission. This pulse can be as large as a normal signal applied to the transistor, which results in an unwanted electronic switching operation. A recent example of how harmful such an event can be was noted in an incident where the key space camera HIFI onboard the ESA space telescope Herschel failed following a SEU in the Local Oscillator Control Unit. This led to an emergency switch-off, which in turn resulted in an overvoltage spike and an overload, leading to permanent failure. Other kinds of single event effects include spurious pulses, permanent destruction of HEXFET transistor arrays, glitches in combinatorial digital circuits, temporary non-functionality caused by SEU bit-flips or mild latchups. The possibility of multiple failure modes due to space radiation generates a particular emphasis on radiation hardening and thorough testing of electronic components before they are sent into orbit. As a consequence, ground radiation hardening tests of electronic circuits and components intended for use in space is critical to the success of space programs. Typically, tested components are irradiated by proton or electron beams using ground-based accelerators, and the failure rates are measured as a function of cumulative radiation dose.
In light of the extreme radiation found in space and certain ground-based facilities such as nuclear power stations, manufacturers of missiles and nuclear power stations have developed systems for testing and hardening electronic circuitry before placing them in functional use. Typically, these tests have involved bombarding the electronic circuitry using particle beams from conventional particle accelerators.
However, ground-based conventional particle accelerators can not reproduce the exponential electron beam distribution spectrum that occurs in space, and a typical approach to ground-based radiation hardening testing involves investigating the impact of radiation at multiple monochromatic energies, and then extrapolating the results to other energies based on models and assumptions. These workaround methods are not only inaccurate, but also laborious and expensive, and sometimes inherently cannot capture the physics of specific situations that arise in space.
The primary deficiency in such ground-based approaches is that the naturally occurring space radiation environment energy spectrum (FIG. 2A) is dramatically different from the output of a conventional Earth-bound accelerator (FIG. 2B) because, on Earth, accelerators based on classical technology do not generate particle energy spectra that follow the exponential distribution found to characterize particle energy spectra in space, but instead give nearly monoenergetic distributions. Conventionally, such Earth based particle acceleration for testing has been done using radiation that is generated by the decay of radioactive materials such as Cobalt-60, in conjunction with conventional particle accelerators which are generally based on a radio-frequency cavity such a synchrotron. Furthermore, scattering of such monoenergetic beams in solid matter (e.g., satellite shielding) reshapes the beam energy distributions to forms that are even more unnatural and thus sometimes poorly suited to reproduce radiation that simulates space radiation and to explore its effects.
For example, consider a monoenergetic electron beam of energy E=5 MeV as produced by a conventional ground-based electron accelerator. Based on calculations with MULASSIS (a Geant4-based multilayered shielding simulation tool), we have evaluated the spectral change when the beam straggles through a mm-scale shielding based on a combination of aluminum and plastic. FIG. 2B shows the results of these calculations. It can be seen that during passage through the shielding, increasing numbers of lower energy electrons are produced, while the 5 MeV peak becomes less pronounced. By comparing FIG. 2A with FIG. 2B, it is evident that the electron spectra to be encountered in space and those producible on Earth by conventional accelerators are very different. In fact, the energy spectra generated on Earth after passing a monoenergetic beam through shielding look diametrically opposite to energy spectra encountered in space. Considering the energy-dependent stopping powers, it can therefore be concluded that such Earth based electron accelerators are far from well suited to simulate space electron radiation.
Thus, due to increasing miniaturization and computerization, and further due to the increasing number and complexity of space missions, the demand for “beam time” for ground-based component testing is ever increasing despite its shortcomings. In addition, due to increasingly complex mission profiles and increasing security needs, the influence of individual effects such as Single Event Effects (“SEE”), is becoming ever more important. Beam time at test facilities capable of testing such effects in wide parameter ranges is becoming ever more expensive.
Consequently, there is an increasing need in the art for an inexpensive and simple method for testing electronic circuits intended for use in space and other high energy radiation environments, that is capable of producing a broad spectrum of high energy particle radiation of multiple types. The present invention addresses these and other needs.